====== F.16 Lifespan ======
[[dido:public:ra:xapend:xapend.f_qos:start| Return to DDS Quality of Service ]]

The LIFESPAN [[dido:public:ra:xapend:xapend.a_glossary:q:qos|QoS]] avoids delivering “stale” data to the [[dido:public:ra:xapend:xapend.a_glossary:a:application|application]].
Each data [[dido:public:ra:xapend:xapend.a_glossary:s:sample|sample]] written by the ''DataWriter'' has an associated ‘expiration time’ beyond which the data should not be delivered to any application. Once the sample expires, the data will be removed from the ''DataReader'' caches as well as from the transient and persistent information caches.

The ‘expiration time’ of each sample is computed by adding the duration specified by the LIFESPAN QoS to the source
timestamp. As described in 2.2.2.4.2.11 and 2.2.2.4.2.12 the source timestamp is either automatically computed by the Service each time the ''DataWriter'' ''write'' operation is called, or else supplied by the application by means of the ''write_w_timestamp operation''.

This QoS relies on the sender and receiving applications having their clocks sufficiently synchronized. If this is not the case and the Service can detect it, the ''DataReader'' is allowed to use the reception timestamp instead of the source timestamp in its computation of the ‘expiration time.’

Source: [[https://www.omg.org/spec/DDS/1.4/PDF | DDS 1.4 Spec]]

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